1. Field of the Invention
The present invention relates to a lighting device for a vehicle, such as an automobile, for presenting a visual indication to other vehicles.
2. Description of the Related Art
A lighting device for a motor vehicle is generally constructed such that light bulbs are mounted in a body of the lighting device (referred to frequently as a lamp body), and a lens with different patterns of lens steps formed thereon is mounted in the front opening of the body. Recently, some types of lighting devices, such a braking lamp, utilize light emitting diodes (LEDs). To obtain an intended light distribution characteristic irrespective of the types of the light source used, a related pattern of steps for refracting light from the light source must be formed in the surface of lens. To realize a lighting device for directing light from the light source in a present direction by refracting light at a large angle by the lens, the refractive index of resin for the lens and restrictions in designing a pattern of lens steps that can be formed in the lens make it difficult to form a pattern to satisfy required light distribution characteristics.
Typical devices other than the formation of lens steps are thus used to obtain a desired light distribution characteristic. For example, the reflector formed on the lamp body is shaped in a predetermined manner, and additional optical parts, such as an inner lens, provided within the lamp body are employed. The result is to make the shape of the lamp body more complicated, to increase the required number of parts, and consequently to increase the cost to manufacture the device. Additionally, the lamp body and the optical parts must be designed and manufactured specifically for every type of lighting device. In other words, it is almost impossible to use common parts for different types of lighting devices.
Accordingly, an object of the present invention is to provide a lighting device which obtains a desired light distribution characteristic by applying a hologram onto a lens of the lighting device, and realizes simplification of construction, reduction of the required number of parts, and thus allows common parts to be used for different types of lighting devices.